Method of preparing rich-mixture aviation fuel



METHOD OF PREPARING RICH- AVIATION FUEL we... 1mm and William 0. Bowen, In. Union, N. J., auignors to Standard Oil Development Company, acorporation of Delaware Application September 4, 1m, .Serial No. 41,164

3 Claims.

This application is a continuation-in-part of application U. S. Serial No. 486,542, filed May 11, 1943, now abandoned.

The present invention relates to improved motor fuels, and more, particularly it relates to improved motor fuels for use in connection with aviation internal combustion motors, particularly when such engines are operated under rich mixture conditions such as used when exceptionally high powers are required (e. g. in takeoff or combat). High octane gasolines may be prepared from a. number of possible sources but the petroleum industry is always striving to improve the octane ratings of the motor fuels designed for use in internal combustion engines, both those employed in automobiles and those employed in aircraft. While the present invenof per gallon, give octane numbers of at least- --1Q0 by the A. S. T. M. aviation .methodt. 'operation [in particular is cbmplicate'dflbygthef fact that there are two distinct andwidelyjdifferent phases of operation, viz., cruising operation and take-off and climb operation. The former is usually carried out under lean conditions (i. e., low' fuel to air ratios) for the purpose ofeconomy. Take-off and climb I are made under rich conditions (i. e., high fuel to air ratios) in order to avoid detonation under the'high power outputs required. It has been found that fuels of the same lean mixture performance may vary widely in resistance to detonation under take-ofi or other rich mixture conditions. It, therefore, does not follow that a complete and highly useful fuel is always produced, in the case of airplane engines, simply because its octane number is ,100 or in excess of 100 by the ordinary A. S. T. M. methods. It

must also have high resistance to detonation under rich mixture conditions. In the laboratory the rich mixture antiknock quality of gasoline is evaluated by determining the maximum permissible knock-free power output the fuel will deliver with high fuel to air ratios in a standard aviation gasoline test engine. This power is expressed in terms of indicated mean effective pressure (hereinafter referred to as IMEP), said pressure being determined in pounds per square inch. For a good aviation fuel to be used in connection with modern supercharged aviation engines, not only must the distillation curve range between about 100 1". and about 300-350 it. with a 'point below about 221 F. (by the ASTM distillation method), with the entire fuel being of an octane number 'of at least 100 by conventional ASTM measuring methods, but in addition this fuel should have an IMEP under rich mixture conditions at least equivalent to that of isooctane (2,2,4-

!0 trimethyl pentane) containing 1.3 cc. of tetraethyl lead per U. 8. gallon. Such fuels are usually blended compositions, that is, they are made up of several components. A typical and highly useful aviation fuel may comprise a base stock of straight run or virgin naphtha having a conventional ASTM octane number of from to to which is added alblate, hydroformed naphtha, stabilized catalytically cracked naphtha, hydrogenated olefin polymers, and the like, having the requisite boiling range to supplement or complement that of the base stock. To this there is usually added a maximum of 4.6 cc. of lead tetraethyl per gallon in orderto raise the octane number to at least by the ASTM aviation method. Such a fuel, while highly useful as proven by actual use in aircraft, is not the perfect fuel for present day supercharged aviation engines, principally because of the fact that it does not have a sufficiently high power output under rich mixture conditions. By reason of the different phases (e. g., take-off and cruising) of aircraft operation, rich mixture performance is just as important an indication of the true worth of an aviation fuel as is the more conventional and standardized octane number rating as heretofore employed for measuring the quality and performance of a particular fuel. As referred to hereinafter, the rich mixture performance of the fuels hereinafter described and which were employed in supercharged test engines was de by the procedure known or without the use of lead 'tetraethyl) but 8180 a rea im rov power output (for take- ;bd; combat and rapi climb conditions) and which is best utilized when the fuel is employed under rich mixture conditions in aviation engines. It is a further object of the invention to so blend an aviation fuel that the base stocks and blending agents employed, when properly blended, give a higher quantity of superior grade aviation fuel than'has heretofore been thought possible. Other objects will be apparent upon a fuller understanding of the invention as. more fully hereinafter described.

Although it has been knownin the past that the polyalk'yl benzenes such as the xylenes were extremely effective antikno'ck agents when added in small amounts to ordinary motor fuels (cf. "Phvsical Constants of the Principal Hydrocarbons." 3rd edition, 1942, by M. P. Doss, Texas Company, pages 75-77, where the octane blending values of the three xylene isomers and higher polyalkyl benzenes are all listed as being greater than 1.00 by conventional ASTM methods), it was. not known that there was a fundamental distinction apparent as between the various isomeric polyalkyl benzenes when these isomers were incorporated in aviation fuels employed under rich mixture conditions in supercharged engines. The startling discovery has been made that in supercharged engines as tested with fuels designed for use therein in accordance with the AFD-3C-rich mixture method, mixtures of polyalkyl benzenes such as ortho, meta and para xylene when added to basic aviation fuels, although tending to increase the IMEP considerably, failed to give a full appreciation in power output of those fuels when compared with thesame fuel to which only meta-xylene and/or para-xylene and/or ethylbenzene or other polyalkyl benzenes (excluding ortho substituted constituents) was added. The present invention is based upon the discovery that aviation fuels for use in supercharged engines under rich mixture conditions are vastly improved if, for example, a Ca aromatic fraction substantially devoid of ortho-xylene is employed in preference to the use of a Cs aromatic fraction containing substantial amounts of ortho-xylene. Similarly, Co and Cm polyalkyl benzene fractions substantially freed of ortho substituted constituents are much preferred over the same Cs and C10 fractions containing the orthosubstituted con.-

' aviation gasoline base stock of octane number.

4. Hydroforming of ramnate from solvent extraction of any aromatic naphtha fraction, e. g.. from aromatization 0r catalytic cracking;

5. Catalytic cracking of gas oils with the distillation of the product thus formed;

6. After-treating and distillation of catalytically cracked naphthas;

7. Thermal cracking and reforming operations;

8. Alkylation of lower boiling aromatics such as benzene and toluene;

9. Cracking, catalytic or thermal, of higher boiling aromatics obtained by solvent extraction;

10. Cycliz'ation and dehydrogenation of ole- 11. Polymerization of acetylene followed by alkylatlon;

12. Isomerization of ortho-xylene in the presence of catalysts such as silica-alumina, etc., to produce mixtures of ortho-,vmetaand para-xylenes;

13. Catalytic aromatization of virgin naphtha fractions;

14. Destructive distillation of wood;

15. From coal tars.

At any event, and regardless of the particular source of the aromatic fractions, the useful blending agent may be isolated from these various polyalkyl aromatic cuts by feeding the same to a distillation column and carefully controlling the overhead product so that the material going overhead'in the case of the xylenes, for example, has a boiling point up to 287 F. at atmospheric pressure while the material withdrawn from the bottom has an initial boiling point of 287-288 F. Such an overhead fraction will be substantially devoid of ortho-xylene in most cases and will be suitable for use as a blending agent in connection with aviation fuels, more particularly those employing base stocks having an original or initial IMEP of at least lbs. per square inch. Substantially pure metaand/or para-xylene may be employed, either as a substantially pure chemical compound obtained by chemical methods, ormixed with an appreciable amount of ethylbenzene which has likewise been found to be effective in increasing the rich mixture rune values of aviation fuels employed in aircraft engines. However, from the cost standpoint it is preferred to' employ the Ca aromatic fractions obtained from the heretofore mentioned sources and isolated in accordance with the distillation procedure hereinbefore mentioned. These cuts may likewise contain considerable quantities of ethylbenzene which, as now known, constitutes a very effective power output improver for aviation fuels. As illustrative of the improvement in aviation fuels when the Ca aromatic fraction is substantially free of ortho-xylene, the following is a typical example:

' Example 1 An AFD-BC-rich mixture antiknock rating was obtained by. adding antiknock blending agent composed on the one hand of a total Cs aromatic cut obtained from a hydroforming operation, and on the other hand an identical cut from which the ortho-xylene had been removed, said blending agents, containing 25% of isopentane, and this mixture added in 17% concentration to an In a second comparative series, the total Ca'aromatic cut was obtained from a catalytic cracking operation and this was compared with the same cut from which the principal quantities of orthoxylene had been removed. The comparative data are as follows:

in order to improve octane number and volatility characteristics of the final fuel. Thus, between Blending Value for Aromatic Blending Agent at 17% Concentration in Base Octane Number Material SO-Rich Mixture *4 cc. Lead Clem- AB'IM Aviation etraothyl/Gal. AS'IM Method +4 cc. IMEP, lbsJsq. Motor of Lead Tetrain. Method ethyl per Gal.

Total C; Aromatic Out from 82% 96% 171 Hydroiorming. Ditto with Ortho-Xylene Out 88 100 -282 Removed. Total vCI Aromatic Out from 90% 100 272 Catalytic Cracking. Ditto with Ortho-Xylene Cut 92% Iso+0.5cc.TEL/ 400 removed. Gal.

Example 1a 2 about and 60% by volume of alkylate such The improvement in the fuel may also be illustrated by another comparison. The removal of ortho-xylene has been found to permit the use of lower concentrations of aromatics in any particular aviation fuel, thus making it easier to meet heating value and other aviation gasoline specifications while at the same time not sacrificin volatility, octane number or power output in the slightest. This advantage becomes even greater as the antiknock level requirement of any par- \ticular aviation fuel is raised. Thus, where a total Ca cut containing the orthoas well as metaand para-xylenes in conjunction with isopentane was added to an aviation fuel having 100 octane number it was found that, in order to give a suitable final aviation blend, 33 volume per cent of the aromatic-isopentane mixture was required to be added. In this particular instance the final aviation blend was equivalent in AFD-3C-rich mixture rating to isooctane plus 2 cc. of lead tetraethyl per gallon. On the other hand, the same octane rating equivalency could be obtained using the same base stock and the same aromatic blending agent, but wherein the ortho-xylene was removed therefrom, if only 22 volume per cent of the aromatic blending agent containing the isopentane were added to the octane number base stock. This represents not only a saving of the ortho-xylene removed, but actually about a 2 volume per cent saving in the total hydroformate requirement.

Any suitable base stock such as those customarily employed in the production of aviation fuels may be employed in this connection, for example, isoparaflinic base stocks or isoparaflinicnaphthenic base stocks such as those prepared by adding synthetic isoparaflins to virgin naphthas. It is preferred that base stocks at least equivalent in AFD-3C-rich 'mixture performance to a blend of 90% S Reference Fuel in M Reference Fuel (equivalent to a mixture of 95 volume per cent 2,2,4-trimethyl pentane 5 vol-ume per cent nheptane) be employed since the greatest utility of the invention resides in the use of such base stocks. Suitable specific base stocks are virgin naphthas, hydroformed naphthas, catalytically or thermally cracked 'naphthas, etc. To these base stocks it is proposed that varying quantities of alkylate, hydropolymer and the like be added as that produced in the ethylation, propyla-tion, butylation or pentylation of isobutane or isopen tane may be employed. Also, the base stock may consist entirely of alkylate, hydropolymer, or hydrocopolymer naphthas. Likewise, because of heat content limitations, volatility requirements and operating difliculties, it is desired that the total amount of aromatics in the aviation fuel be restricted to less than 40 volume per cent, preferably less than 25 volume per cent. Lead tetraethyl or some other suitable antiknock agent is usually added in order to increase octane number, and under the present U. S. Army specifications as high as 4.6 cc. of lead tetraethyl per gallon may be employed, though if it is desired less lead and more aromatics may be added to compensate for the decreased amount of lead. The Ca fraction employed in conjunction with the present invention--and, as indicated. this Ca fraction is substantially free of ortho-xylene-may be employed in an amount ranging between about 1 and about 40 volume per cent, with the amount of crtho-xylene present being limited to less than 6 weight per cent of the total Ca aromatic hydrocarbon fraction and preferably being less than 2 weight per cent thereof. Ideally. of course, a Cs aromatic fraction entirely devoid of ortho-xylene is preferred, but in commercial practice it is difficult to economically free such a crude Ca fraction of all of the ortho-xylene. The same ranges hold for the Ca fraction or for mixtures of Ca and C9 fractions.

The invention will be more readily understood from the drawing which represents in diagrammatic form one method by which the process of the invention may be accomplished.

Referring to the drawing, numeral 1 represents a conversion zone in which a hydrocarbon fraction rich in aromatic hydrocarbons is produced. The conversion zone may be a hydroforming zone, a catalytic cracking zone, a steam cracking zone, an isomerization zone. etc. It is known that hydrocarbon fractions rich in aromatics may be produced by the above means among others.

When the conversion zone is operated as a hydroformer, a naphtha feed containing 15 to 50% naphthenes boiling in the range of about 200 F. to 400 F., preferably 200 F. to 325 F., is introduced thereto via line 2. The hydroformer oper- 7 ates at atmospheric to 500 pounds per square inch pressure, preferably 200 to 250 pounds per square inch. and at a temperature of 800 F. to 1050" F. The hydroforming operation is carried out in the presence of a gas rich in free hydrogen. 500 to 5000 cubic feet of gas containing 20 to 90 mol percent free hydrogen are employed per barrel of naphtha. The heavy end of the aromatic product boiling in the range of 170 F. to 335 F., contains about 80 to 80% aromatic hydrocarbons boiling in the range of Ca and above. The hydroforming catalyst employed is one comprising the oxides or sulfides of the fourth. fifth, sixth, and eighth groups of the periodic table, especially the oxides of vanadium. molybdenum, chromium, tungsten, cobalt and nickel, either alone or in mixtures, or in the presence of a carrier, for example, aluminum oxide. alumina gel, clay, etc.

When the conversion zone is operated as a steam cracker, a heavy naphtha or vaporizable gas oil is fed thereto under conversion conditions of 1200 F. to 1600 F., 80 to 90 mol percent steam, and substantially atmospheric pressure. A short contact time is employed and the product is immediately quenched to 600 F. to 1000 F.

In the catalytic crackingioperation a gas oil feed is fed to the conversion zone, and conversion conditions of 800 F. to 1000 F., pressures substantially atmospheric, or slightly above, and a catalyst are employed. The catalyst is preferably a clay such as acid treated bentonite, Super-Filtrol, synthetic silica alumina gel, synthetic silica and magnesia gel, etc. In a stationary bed about one volume of liquid oil per volume of catalyst per hour is fed to the unit. In a fluid system 3 to 20 parts of catalyst per one of oil may be employed. The product from the catalytic cracker contains a C7+ fraction in the gasoline range in which aromatics are found in greater than approximately 50 volume percent concentration.

The product emerging from the conversion zone and being rich in aromatic hydrocarbons is fed via line 3 to fractionator 4. In fractionator 4 the product is fractionated into a top out boiling up to 260 F., which is removed via line 5, an intermediate fraction boiling in the range of 260 F. to 330 R, which is removed via line 1,

traction zone 8. In extraction zone 8 the aro-.

matic hydrocarbon content of the fraction is extracted by means of a selective solvent such as $02, nitro-benzene, cresol. furfural, phenol, or any of the well known solvents or mixtures thereof. To this end the solvent is introduced at a point 9, and the mixture extracted in countercurrent operation. At this point it should be noted that if the solvent is lighter than the feed, the positions of the feed and the,solvent may be reversed. In any event the material in the extraction zone separates into an extract phase and a rafiinate phase. For purposes of illustration, the raiiinate phase is removed from the extraction zone via line It and may be employed for further processing. For example, if the conversion zone is operated as a catalytic cracking operation, the rafllnate after removal of solvent therefrom is excellent feed for a hydroforming operation. The extract containing the aromatic hydrocarbons is removed from the extraction zone via line I I and fed to mne l2 where the solvent is removed therefrom via line it such as by fractionation. The aromatic fraction is removed from the zone [2 via line I4, and introduced into a fractionator II. The fractionator i5 is so operated as to take overhead via line It an aromatic fraction boiling between 260 F. and 288 F. An intermediate fraction is removed from the tower via line I]. This intermediate fraction boils in the range of 288 F. to 300 F., while the bottoms removed from the fractionator via line I. consist of aromatic hydrocarbons boiling in the range of 300 F. to 330 F. The fractionation of the aromatic fraction may be accomplished in one, two. or more fractionation zones as efficiency and economy dictate.

If desired, part or all of the fractions being removed via lines l6 and It may be removed via lines l9 and 20 respectively, to storage vessel 2|. The fraction boiling in the range of 288 F. to 300 F., is rich in ortho-aromatic components and may be isomerized in isomerization zone 23 to the corresponding meta and para components. or may be recycled to the conversion zone via lines 22 and 25 for further conversion to more desirable fractions when the conversion zone is operating as an isomerizer.

In the isomerization zone 23, the aromatic fraction boiling in the range of 288 F'. to 300 F., and introduced thereto via line 22, is contacted with a suitable isomerization catalyst at a temperature in the range of about 500 F. to about 1100 F., preferably 750 F. to 1025 F. A feed throughput of 0.4 to 6.0 liquid volumes per volume of catalyst mass per hour is employed. Superatmospheric pressure may be employed to maintain liquid phase operation, if desired. However, the process may also be carried out in the vapor phase generally at pressures from 1.5 to 10 atmospheres. Suitable catalysts are synthetic alumina-silica gels containing an oxide promoter such as is described in U. S. 2,403,- 757 to Edward D. Reeves; hydrogen fluoride; aluminum halide-hydrogen halide mixtures; BF3; BFz-hydrates, etc. A preferred catalyst is a plural synthetic alumina-silica gel containing small amounts of at least one oxide promoter selected from the groupconsisting of boron oxide, thoria, zirconia and magnesia. A product richer in meta and para substituted aromatic hydrocarbons boiling in the range of 260 F. to 288 F. than the isomerization feed is recovered from the isomerization zone via line 24 and sent to fractionator 4 via line- 3 for further work-up with the original aromatic hydrocarbon-rich fraction. The bottom of zone 23 may act as a settler and heavy products such as tar, etc., may be removed therefrom via line 26.

As illustrative of the type of fuels which are preferred and find unexpected utility in rich mixture operation of supercharged aviation engines, the following blends were prepared and tested as described. It is to be distinctly understood, however, that the invention is not limited to the particular blends nor to the particular tests herein outlined, but these examples of test runs are simply illustrative of the character of the invention.

Example 2 A blend was prepared having the following composition:

Component:

Hydroformed aromatics fraction blending agent (containing 25 volume per cent extraneous isopentane to maintain proper vapor pressure) volume per cent 26.7 Net concentration of hydroformed aromatics fraction -volume per cent 20.0

Base stock (46% Pecos virgin naphtha,

54% alkylate blending agent) 2 volume per cent 73.3 To this blend was added 4 cc. of TEL per gallon. The fuel thus prepared had the following properties:

Gravity, API 62.8

Reid vapor pressure, lbs/sq. in. 6

ASTM distillation, per cent condensed, F.:

1 C, aromatics fraction emplozyed in'Example 2 was produced by hydroforming a 200- 70. 13. East Texas virgin naphtha under the following conditions:

Operatin pressure, s. i 200 Space ve ocity, v./v./ r 0.50 Reaction temperature, F 960 Recycle gas rate, CF/bbl "I 2560 The C aromatics fraction had the following composition, based on analysis by fractional distillation and ultra-violet spectrophotometry Weight per cent Ethylbenzene 7 Para xylene 12 Meta-xylene rtho xylene 8 Higher aromatics Total aromatics 92 I *(iharacteristlcs of the base stock employed in Exanr pie Gravity, AII 70.1 Reid vapor ressure, lbs/sq. in 6.2 ASTM dist llation, per cent condensed. F.

Initial boiling point 114 10% 143 50% 188 90% 236 Final boiling poin 281 Per cent recovery 98.n Per cent residue 0.6 Per cent loss 0.9 ASTMM0tor Method octane number. clear 84 ASTMMotor Method octane number 4 cc. TEL/ga.l 100 ASTM aviation octane number 4 cc. TEL/gal 100 AFD-ZiC-rich mixture rating, lbs. sq.

in., 4 cc. TEL/gal 198 IMEP, equivalent to isooctane plus 1.1 cc. TEL/gal.

Example 3 Component (produced as in Example 2) Hydroformed Cs aromatics fractions.

from which ortho-xylene has been removed by fractional distillation, blending agent (containing 25% ex- Component (produced as in Example 2) :Con.

traneous isopentane to maintain proper vapor pressure) volume per cent 26.7 Net concentration of hydroformed aromatics fraction volume per cent 20.0 Base stock (same as employed in Example 2) volume per cent 73.3

To this blend was added 4 cc. of TEL/gal. The fuel thus prepared had the following properties: Gravity API Reid vapor pressure, lbs/sq. in. ASTM distillation, per cent condensed, F.:

Initial Boiling point 109 10% 145 50% 211 268 Final boiling point 286 Per cent recovery 98.0 Per cent loss 1.5 Per cent residue 0.5 ASTM-motor method octane number 99 ASTMaviation octane number AFD 3C rich mixture rating,

lbs/sq. in 220IMEP,equivalent to 15000- tane plus 2.4

c. c. TEL/gal.

Analysis or the Cg aromatics fraction employed in Example 3. (By fractional distillation and ultra-violet spectrophotometry method.)

Analysis Ave. oi 1 2 l and 2 Ethylbenzene Weight Per Cent Para-Xylene, Weight Per cent Meta-Xylene, Weight Per cent Ortho-Xylene Weight Per Cent. Total Aromatics, Weight Per Cent.

To this blend was added 4 cc. of TEL/gal.

Characteristics of base stock employed in Example 4. Gravity, API 70.0 Reid vapor ressure, lbs/sq. in ASTM dist llation, per cent condensed, F.:

Initial boiling point 107 90% 238 Final boiling point 284 Per cent recovery 98.0 Per cent loss 1.0 Per cent residue 1.0 ASTMM0tor Method octane number. clear 84 ASTMMotor Method octane number 4 cc. TEL/gal 100 ASTMaviation octane number+ 4 cc. TEL/gal Isooctane 0.01 AFD-3C'rich mixture rating 4 cc.

TEL/gal, lbs./sq. in 200 IMEP, equivalent to isooctane 1.1

cc. TEL/ gal.

11 The fuel thus prepared had the following properties:

Gravity, API 65.4 Reid vapor pressure, lbs/sq. in- 6% AS'IM distillation, per cent condensed, F.:

Initial boiling point 108 I 10% 144 50% 204 90% 263 Final boiling point 293 Per centrecovery 96.0 Per cent loss 1.0 Per cent residue 1.0 AB'IM-motor method octane number 100 ABTM-aviationoctanenumber- Isooctane+0.02

- cc. TEL/gal. AFD-SC-rich mixture rating,

lbs/sq. in. 217IMEP,equivalent to isooctane plus 2.0 c. c. TEL/gal.

The methods of test used to evaluate the abovementioned blends are those recognized by the American Society for Testing Materials (ASTM) or the Army-Navy Specification Board and are designated by them as follows:

Gravity, 'API u ds ihfige igfnation D287- ASTM distillation Aslalidugzgifnation D86- Reid vapor pressure ASTM Designation D323- 42 (1942) Octane number:

A8TMMotor Method-" ASTM Designation D357- 42'1 (1942 ASTMAviation Method- ASTM Designation D614- AFD3C Supercharged Performance Method--- Army-Navy Specification gie thgd AN-VV-F- centration volume per cent 26.7 Net ortho-xylene content volume per cent-.. 20.0

Base stock (45% Pecos virgin naphtha,

55% alkylate blending agent) 3 volume per cent 73.3 To this blend was added 4 cc. of TEL/gal.

Analysis or ortho-xyleue used in Example 5 (5 ultrav io lgg spectrophotometry) :98 weight per cen ortho- Characteristics of base stock used in Example 5. Gravity, API 70.5

Reid va or resure, lbs./sq. in-..- ASTM istilation, per cent condensed, F.:

Initial boiling point 111 153 50% 209 90% 248 Final boiling point 298 ASTMMotor Method octane number, clear 83 ASTM-aviation octane number 4 cc. TEL/gal Is c tfine 0.01 cc.

a AFD-3C-rich mixture rating 4 cc. /g

TEL/gaL, lbs./sq. in 192 IMEP. equivalent to isooctane 0.7

cc. TEL/gal.

12 The fuel thus prepared had the following erties:

Gravity, API 61.6 Reid vapor pressure. lbs/sq. in. 6

ASTM distillation, per cent condensed, F.:

Pure para-xylene, C. P. grade, added as blending agent containing 25% extraneous iso-pentane to maintain proper vapor pressure: 1

Para-xylene blending agent concentration volume per cent 26.7 Net para-xylene content volume per cent.-- 20.0 Base stock (same as employed in Example 5) volume per cent 73.3

To this blend was added 4 cc. of TEL/gal.

The fuel thus prepared had the following properties:

Gravity, API 62.8 Reid vapor pressure, lbs/sq. in- 6 ASTM distillation, per cent condensed, F.:

Initial boiling point 102 10% 145 50% 225 270 Final boiling point 295 ASTM-aviation octane num- Isooctane plus 0.2 cc. AFD 3C rich mixture rating,

lbs/sq. in. 266IMEP,equivalent to 180%- taneplusmore t h a n 6 cc. TEL/gal.

Analysis of para-x lene used in Example 6 (b ultraziyolleet spectrophotomery)=98+ weight per cen t para- Example 7 Component:

Pure meta-xylene, C. P. grade, added as blending agent containing 25% extraneous isopentane to maintain proper vapor pressure: 1

Meta-xylene blending agent concentration..- vo1ume per cent 26.7 Net meta-xylene content volume per cent 20.0

Analysis of meta-xylene used in Exam 1e 7 b ult go leelfe spectrophotometry)= weight ger ce nt me t answer 13 Componentz-Continued.

Base stock (45% Pecos virgin naphtha.

55% alkylate blending agent) volume per cent 73.3

To this blend was added 4 cc. of TEL/gal. The fuel thus prepared had the following properties:

Characteristics of base stock used in Example 7 Gravity, API 09.4 Reid vapor ressure, lbs./sq. in--- 6% ASTM dist llation, per cent condensed, F.

Iraltial boiling point 9O Final boiling point ASTMMotor Method octane number. clear 82 ASTMaviat1on octane number 4 cc. TEL/gal 99 AFD-3C-rich mixture rating 4 cc.

TEL/gal 198 IMEP, equivalent to isooctane 1.0 cc.'TEL/gal.

Example 8 A blend was prepared having the following composition:

Component:

C'z-Cio aromatics fraction (225-350 F.) from catalytic cracked gasoline, solvent extracted. (Added as blending agent containing 25% extraneous isopentane to maintain vapor pressure) volume per cent 24.3 Net concentration of 225-350 F'. fraction volume per cent 17.0 Base stock (50% Pecos virgin naphtha,

50% alkylate blending agent) volume per cent 75.!

(I -C", aromatics fraction emplgzed in Example 8 was produced by fluid catalytically cra lng Tinsley gas oil at 975 F. reactor temperature, 5.4 catalyst/oil ratio. 65% conversion, over alumina-silica gel catalyst. The 225-350" F. fraction from catalytic cracking was solvent extracted with S and acid-treated with 20#/bbl. of 98% 113804- The C7-C aromatics fraction thus obtained contained a total of 96 volume per cent aromatics. h: a refractive index (sodium line at 20 C.) of 1.4963. and an Al'l gravity of 31.7 and contained approximately 11 volume per cent toluene, 43.0 volume per cent xylenes and ethyl benzene, 42 volume per cent of Cir'Cm alkylaromatics.

(haracteristics of the base stock employed in Example Gravity API 69,5 Reid vapor ressure. lbs/sq. in 6.5 ASTM dist llation, per cent coudcnsed, F.

Initial boiling point 122 AFD-3C-rich mixture rating 4 cc.

TEL/gaL, 1bs./sq in 177 IMEI, equivalent to isooctane 0.5

cc. TEL/gal.

14 To this blend was added 4 cc. TEL/gal. The fuel thus prepared had the following properties:

ASTM-aviation octane numerties: Isooctane plus 0.01 cc. TEL/ gal. AFD 3C rich mixture rating,

lbs/sq. in. IBQIMERequivalent to tametane plus 1.0 cc. TEL/gal.

Example 9 A blend was prepared as follows:

Component:

1,3,5 trimethylbenzene (mesitylene) fraction from fractionation of C7-Cro aromatics fraction employed in Example 8. (Added as blending agent containing 25% extraneous isopentane to maintain proper vapor pressure) volume per cent Net concentration of mesitylene fraction volume per cent.-- Base stock (same as employed in Example 8) volume per cent 75.?

To this blend was added 4 cc. of TEL/gal. The fuel thus prepared had the following properties:

ASTM-aviation octane number Isooctane+0 04 cc. TEL/gal.

AFD-SC-rich mixture rating,

lbs/sq. in -199 IMEP,

equivalent to isooctane+ 1.3 cc. TEL/ gal.

Mesitylene fraction em loyed in Example 9 contained 99 volume per cent aromat cs. It had a refractive index at 20 C. of 1.4988, and an API gravltv of 31.8. Its Cottrell boiling range was from 328 to 329 F.

Example 10 A blend was prepared as follows:

ASTMaviation octane number Isooctane 0.01

cc. TEL/gal. AFD-3C-rlch mixture rating,

lbs./sq. in .170 I M E P, equivalent to isooctane+ 0.15 cc. TEL/ gal.

Pseudocurnene fraction employed in Example 10 contained 99 volume per cent aromatics. It had a refractive index at 20 C. of 1.5033, and an API gravity of 30.7 Its Cottrell boiling range was trom 335 to 336 F.

Although the invention has been described with reference to C; and C9 polyalkyl aromatic fractions in which those constituents having ortho positioned alkyl radicals have been substantially completely removed, it is to be distinctly understood that the invention is not limited to these particular compounds as set forth in the specific examples. Thus, although a crude xylene fraction containing ortho, meta, and para xylene may be employed in the production of fuels according to the present invention, when the ortho xylene is substantially removed therefrom, there are still other specific compounds which may also be employed in the spirit of the present invention. A Co aromatic fraction which may contain n-propyl benzene, isopropyl benzene, the trimethyl benzenes and the ethyl toluenes, may be employed if the mixture is treated to separate out all or substantially all of the ortho substituted components. There are three trimethyl benzenes, one of which, namely, 1,3,5- trimethyl benzene, known as mesitylene. comes within the scope of the present invention. The 1,2,3-trimethyl benzene and 1,2,4-trimethyl benzene are not particularly adapted for use in the preparation of fuels according to the present in vention since they both contain ortho substituted methyl groups. Likewise, 2-ethyl toluene is to be excluded, whereas 3-ethyl toluene and 4-ethyl toluene are good blending agents for aviation fuels.

It will be understood that several modifications are readily suggested and it is intended that these modifications which are familiar to those skilled in this art be and here are part of the description.

Having thus fully described and illustrated the character of the invention, what is claimed as new and useful and desired to be secured by Letters Patent is: p

1. A method of preparing high quality, rich mixture aviation fuel which comprises fractionating an aromatic hydrocarbon-containing gasoline fraction to obtain a fraction containing Cs and Ca inclusive aromatic hydrocarbons, including ethyl benzene, ortho, meta, and para xylene, mesitylene and pseudocumene, extracting the said aromatic hydrocarbons from the non-aromatic hydrocarbons in the C8-C9 fraction, removing from said extracted aromatic hydrocarbons the ortho-substituted Cs and Cs aromatic hydrocarbons, and blending the remaining aromatic hydrocarbons with aviation gasoline base stock having a lower octane number than any one of the aromatic hydrocarbons blended therewith to obtain a gasoline containing less than 6 weight per cent of ortho constituents based on the total aromatic hydrocarbons present in the blend.

2. Process according to claim 1, in which the final gasoline product contains less than 2 weight pm cent of the ortho-substituted Cs and C9 hydrocarbons based on the total aromatic hydrocarbons in the blend.

3. A method of preparing a high quality, rich mixture aviation fuel which comprises fractionating an aromatic hydrocarbon-containing gasoline fraction in a first fractionating zone to obtain a fraction boiling within the limits of about 225 and about 35091. containing C1 to C10 inclusive aromatic hydrocarbons, including toluene, ethyl benzene, ortho, meta and para xylenes. mesitylene, and pseudocumene, solvent extracting the said aromatic hydrocarbons from said C1 to C10 fraction, fractionally distilling the resulting extracted aromatic hydrocarbons in a second fractionation zone to separate therefrom a mesitylene fraction having an initial boiling point of about 328 F., a refractive index at 20 of about 1.4988 and an API gravity of about 31.8, and blending this fraction with isopentane, virgin naphtha, and alkylate in the proportions of mesitylene fraction 17.0%, isopentane 7.3%, virgin naphtha 37.85%, alkylate 37.85%, and combining therewith about 4 cc. tetraethyl lead per gallon to give a fuel having an IMEP of 199equivalent to isooctane plus 1.3 cc. of tetraethyl lead per gallon.

WALTER A. HERBST. WILLIAM c. HOWELL, Ja.

REFERENCES CITED TY 3 following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,305,026 Munday Dec. 15, 1942 2,380,279 Welty July 10, 1945 2,425,559 v Passino et al. Aug. 12, 1947 OTHER REFERENCES 

1. A METHOD OF PREPARING HIGH QUALITY, RICH MIXTURE AVIATION FUEL WHICH COMPRISES FRACTIONATING AN AROMATIC HYDROCARBON-CONTAINING GASOLINE FRACTION TO OBTAIN A FRACTION CONTAINING C8 AND C9 INCLUSIVE AROMATIC HYDROCARBONS, INCLUDING ETHYL BENZENE, ORTHO, META, AND PARA XYLENE, MESITYLENE AND PSEUDOCUMENE, EXTRACTING THE SAID AROMATIC HYDROCARBONS FROM THE NON-AROMATIC HYDROCARBONS IN THE C8-C9 FRACTION, REMOVING FROM SAID EXTRACTED AROMATIC HYDROCAR- 